This invention relates to nickel-base high temperature superalloys particularly useful for applications at temperatures in the range of about 1800.degree. - 2000.degree. F. but not restricted to these temperatures. The subject alloys, compared to the state-of-the-art superalloys such as IN-100 (AMS 5397), IN-713C (AMS 5371), MAR-M246, INCO 738 and others, have comparable or better high temperature properties, such as stress rupture life and the like, but contain relatively small amounts of expensive, strategic elements. Furthermore, the alloys are lower in raw material cost per pound and have a lower density than most of the state-of-the-art superalloys. Also, the property of "inverse precipitation" allows these alloys to be more readily machinable at room temperature than the state-of-the-art superalloys because the subject alloys exhibit their high strength only at high temperatures. In contrast, the commercial state-of-the-art superalloys possess exceptionally high strength at room temperatures so that the remnant strength at high temperatures is sufficient for the high temperature use. However, such alloys are usually difficult to machine and work at room temperature.
On the other hand, the subject alloys possess room temperature properties which are lower than comparable state-of-the-art superalloys because at room temperature the alloys of this invention possess a structure which is characterized by a matrix consisting essentially of Ni.sub.x Al.sub.y wherein x varies between about 2.5 to 3.5 and y varies between about 0.75 to 1.25. At elevated temperatures, depending on the particular composition, a precipitate forms within the matrix comprised of Ni.sub.x' Al.sub.y' wherein x' and y' both vary between about 0.75 to 1.25. Contrast this with the typical superalloy in which the structure consists of a gamma matrix, usually nickel solid solutions for example, and a precipitate of, for example, gamma prime i.e., Ni.sub.3 Al.sub.1, present at lower temperatures in stable conditions but which gradually become unstable and tend to dissolve in the matrix at high temperatures. As a result, the subject alloys are usable up to 90% of their absolute melting temperature whereas the state-of-the-art superalloys' use is mostly restricted to about 75-80% of their absolute melting temperature.
The alloys of this invention partially replace nickel and/or aluminum with relatively small amounts of one or more of chromium, titanium, cobalt, molybdenum, tantalum, tungsten, beryllium and columbium, individually or in various combinations. Also, the alloys contain small amounts of rare earths such as mischmetal and small amounts of boron and zirconium. The structure at room temperature shows widespread carbides and occasional boride and nitride phases in a matrix of gamma prime (Ni.sub.x Al.sub.y) phase.